Support getSize and getSizes

Author: tangbc

README.md

@@ -283,6 +283,10 @@ Here are some usefull public methods you can call via [`ref`](https://vuejs.org/
 
 * `scrollToOffset(offset)`: manual set scroll position to a designated offset.
 
+* `getSize(id)`: get the designated item size by id (from data-key value).
+
+* `getSizes()`: get the total number of stored (rendered) items.
+
 
 ## Attentions
 

src/index.js

@@ -76,6 +76,16 @@ const VirtualList = Vue.component('virtual-list', {
   },
 
   methods: {
+    // get item size by id
+    getSize (id) {
+      return this.virtual.sizes.get(id)
+    },
+
+    // get the total number of stored (rendered) items
+    getSizes () {
+      return this.virtual.sizes.size
+    },
+
     // set current scroll position to a expectant offset
     scrollToOffset (offset) {
       const { root } = this.$refs